Digging into my Photos library on my Mac, It doesn't seem so.
I have a live photo taken on my iPad Pro 10.5, which when I dive down into the Masters folder to find, it is saved as a .heic, but only seems to be a still image.
When I go across into the resources/media/master folder, and tracked down all files with the same creation date, I found a matching mov file, just the way Live Photos were previously saved as jpg/mov pairs.
I popped the mov into MediaInfo, it is in hevc, and weighs in at 2.55MB, while the heic is 1.3MB, so it looks like Apple is not packing them together in a single file, at least not yet. Perhaps they plan to do so in the future, but not until there is wider adoption of the HEIF format, or more products out there with HEVC hardware support...? Anyone's guess at this point.